Support use case where exception stack trace frame contains no 'file'

**Description**
There are instances when a stack trace frame may not specify a file/line number. This change will print "[internal function]" instead--this is the same behavior as `Exception::getTraceAsString()`:

```
#0 [internal function]: SomeClass->someMethod()
```

**Functional Test**
Throw an exception and observe no `Undefined index: file` error when file is not set